1. Field of the Invention
The present invention relates generally to a communication system using a multihop relay scheme, and more particularly to a method and system for selecting a relay station by a mobile station.
2. Description of the Related Art
Wireless mobile communication systems are currently evolving from Third-Generation (3G) to Fourth-Generation (4G) mobile communication systems. Research is being conducted to increase system capacity and extend a wireless transmission range, i.e., service coverage, in the 4G mobile communication systems. To do so, a multihop scheme has been proposed. When a channel state between a Base Station (BS) and a Mobile Station (MS) is poor, the multihop scheme can form a multihop relay path through a Relay Station (RS) by installing the RS between the BS and the MS. The MS can receive a radio channel having a good state through the multihop relay path. Further, when the multihop relay scheme is used for the MS located inside/outside a cell boundary at which a channel state is poor, the MS can receive a data channel at a higher rate and can extend cell service coverage in terms of the system.
FIG. 1 illustrates a communication system using the conventional multihop relay scheme.
Referring to FIG. 1, the multihop relay communication system has a multicell structure including a cell 100 covered by a BS 110, a cell 140 covered by a BS 150, a cell 130 covered by an RS 120 and a cell 170 covered by an RS 160. Multiple MSs are present in the cells 100, 130, 140 and 170. Herein, the RSs 120 and 160 can be located inside/outside the cell areas of the BSs 110 and 150 and can relay signals of the BSs 110 and 150 to MSs 121, 123, 161 and 163. If an area in which a signal of an RS such as the RS 160 can be received partially overlaps with a cell area of a specific BS even when the RS is not located inside the cell area of the specific BS, the RS can receive a signal of the specific BS.
As described above, an RS can relay a signal between a BS and an MS located outside the cell area of the BS to extend the cell coverage or can relay the signal between a BS and an MS located inside the cell area of the BS to increase the system capacity. That is, the RS not only can relay a signal of the MS located outside the cell area, but also can relay a signal of the MS located inside the cell area, thereby increasing the system capacity. Thus, the MS should be able to select the proper RS to extend cell coverage and increase system capacity.